Dual spin valve sensor with a longitudinal bias stack

ABSTRACT

A dual spin valve (SV) sensor is provided with a longitudinal bias stack sandwiched between a first SV stack and a second SV stack. The longitudinal bias stack comprises an antiferromagnetic (AFM) layer sandwiched between first and second ferromagnetic layers. The first and second SV stacks comprise antiparallel (AP)-pinned layers pinned by AFM layers made of an AFM material having a higher blocking temperature than the AFM material of the bias stack allowing the AP-pinned layers to be pinned in a transverse direction and the bias stack to be pinned in a longitudinal direction. The demagnetizing fields of the two AP-pinned layers cancel each other and the bias stack provides flux closures for the sense layers of the first and second SV stacks.

CROSS REFERENCE TO RELATED APPLICATION

U.S. patent application Ser. No. 10/116,017, entitled DUAL MAGNETICTUNNEL JUNCTION SENSOR WITH A LONGITUDINAL BIAS STACK, was filed on thesame day, owned by a common assignee and having the same inventors asthe present invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates in general to spin valve magnetic transducers forreading information signals from a magnetic medium and, in particular,to a dual spin valve sensor with a longitudinal bias stack between firstand second spin valve stacks of the dual sensor.

2. Description of the Related Art

Computers often include auxiliary memory storage devices having media onwhich data can be written and from which data can be read for later use.A direct access storage device (disk drive) incorporating rotatingmagnetic disks is commonly used for storing data in magnetic form on thedisk surfaces. Data is recorded on concentric, radially spaced tracks onthe disk surfaces. Magnetic heads including read sensors are then usedto read data from the tracks on the disk surfaces.

In high capacity disk drives, magnetoresistive (MR) read sensors,commonly referred to as MR sensors, are the prevailing read sensorsbecause of their capability to read data from a surface of a disk atgreater track and linear densities than thin film inductive heads. An MRsensor detects a magnetic field through the change in the resistance ofits MR sensing layer (also referred to as an “MR element”) as a functionof the strength and direction of the magnetic flux being sensed by theMR layer.

The conventional MR sensor operates on the basis of the anisotropicmagnetoresistive (AMR) effect in which an MR element resistance variesas the square of the cosine of the angle between the magnetization inthe MR element and the direction of sense current flowing through the MRelement. Recorded data can be read from a magnetic medium because theexternal magnetic field from the recorded magnetic medium (the signalfield) causes a change in the direction of magnetization in the MRelement, which in turn causes a change in resistance in the MR elementand a corresponding change in the sensed current or voltage.

Another type of MR sensor is the giant magnetoresistance (GMR) sensormanifesting the GMR effect. In GMR sensors, the resistance of the MRsense layer varies as a function of the spin-dependent transmission ofthe conduction electrons between magnetic layers separated by anon-magnetic spacer layer and the accompanying spin-dependent scatteringwhich takes place at the interface of the magnetic and nonmagneticlayers and within the magnetic layers.

GMR sensors using only two layers of ferromagnetic material (e.g.,Ni—Fe) separated by a layer of nonmagnetic material (e.g., copper) aregenerally referred to as spin valve (SV) sensors manifesting the SVeffect.

FIG. 1 shows a prior art SV sensor 100 comprising end regions 104 and106 separated by a central region 102. A first ferromagnetic layer,referred to as a pinned (or reference) layer 120, has its magnetizationtypically fixed (pinned) by exchange coupling with an antiferromagnetic(AFM) layer 125. The magnetization of a second ferromagnetic layer,referred to as a free (or sense) layer 110, is not fixed and is free torotate in response to the magnetic field from the recorded magneticmedium (the signal field). The free layer 110 is separated from thepinned layer 120 by a nonmagnetic, electrically conducting spacer layer115. Hard bias layers 130 and 135 formed in the end regions 104 and 106,respectively, provide longitudinal bias fields for stabilizing the freelayer 110. Leads 140 and 145 formed on hard bias layers 130 and 135,respectively, provide electrical connections for sensing the resistanceof SV sensor 100. In the SV sensor 100, because the sense current flowbetween the leads 140 and 145 is in the plane of the SV sensor layers,the sensor is known as a current-in-plane (CIP) SV sensor. IBM's U.S.Pat. No. 5,206,590 granted to Dieny et al., incorporated herein byreference, discloses a SV sensor operating on the basis of the GMReffect.

Another type of GMR sensor is an antiparallel (AP)-pinned SV sensor. TheAP-pinned SV sensor differs from the simple SV sensor in that anAP-pinned structure has multiple thin film layers instead of a singlepinned layer. The AP-pinned structure has an antiparallel coupling (APC)layer sandwiched between first and second ferromagnetic pinned layers.The first pinned layer has its magnetization oriented in a firstdirection by exchange coupling to the antiferromagnetic (AFM) pinninglayer. The second pinned layer is immediately adjacent to the free layerand is antiparallel exchange coupled to the first pinned layer becauseof the minimal thickness (in the order of 8 Å) of the APC layer betweenthe first and second pinned layers. Accordingly, the magnetization ofthe second pinned layer is oriented in a second direction that isantiparallel to the direction of the magnetization of the first pinnedlayer.

The AP-pinned structure is preferred over the single pinned layerbecause the magnetizations of the first and second pinned layers of theAP-pinned structure subtractively combine to provide a net magnetizationthat is much less than the magnetization of the single pinned layer. Thedirection of the net magnetization is determined by the thicker of thefirst and second pinned layers. A reduced net magnetization equates to areduced demagnetization field from the AP-pinned structure. Since theantiferromagnetic exchange coupling is inversely proportional to the netmagnetization, this increases exchange coupling between the first pinnedlayer and the antiferromagnetic pinning layer. The AP-pinned SV sensoris described in commonly assigned U.S. Pat. No. 5,465,185 to Heim andParkin which is incorporated by reference herein.

Another type of magnetic device currently under development is amagnetic tunnel junction (MTJ) device. The MTJ device has potentialapplications as a memory cell and as a magnetic field sensor. The MTJdevice comprises two ferromagnetic layers separated by a thin,electrically insulating, tunnel barrier layer. The tunnel barrier layeris sufficiently thin that quantum-mechanical tunneling of chargecarriers occurs between the ferromagnetic layers. The tunneling processis electron spin dependent, which means that the tunneling currentacross the junction depends on the spin-dependent electronic propertiesof the ferromagnetic materials and is a function of the relativeorientation of the magnetizations of the two ferromagnetic layers. Inthe MTJ sensor, one ferromagnetic layer has its magnetization fixed, orpinned, and the other ferromagnetic layer has its magnetization free torotate in response to an external magnetic field from the recordingmedium (the signal field). When an electric potential is applied betweenthe two ferromagnetic layers, the sensor resistance is a function of thetunneling current across the insulating layer between the ferromagneticlayers. Since the tunneling current that flows perpendicularly throughthe tunnel barrier layer depends on the relative magnetizationdirections of the two ferromagnetic layers, recorded data can be readfrom a magnetic medium because the signal field causes a change ofdirection of magnetization of the free layer, which in turn causes achange in resistance of the MTJ sensor and a corresponding change in thesensed current or voltage. IBM's U.S. Pat. No. 5,650,958 granted toGallagher et al., incorporated in its entirety herein by reference,discloses an MTJ sensor operating on the basis of the magnetic tunneljunction effect.

FIG. 2 shows a prior art MTJ sensor 200 comprising a first electrode204, a second electrode 202, and a tunnel barrier layer 215. The firstelectrode 204 comprises a pinned layer (ferromagnetic pinned layer) 220,an antiferromagnetic (AFM) pinning layer 230, and a seed layer 240. Themagnetization of the pinned layer 220 is fixed through exchange couplingwith the AFM layer 230. The second electrode 202 comprises a free layer(ferromagnetic free layer) 210 and a cap layer 205. The free layer 210is separated from the pinned layer 220 by a nonmagnetic, electricallyinsulating tunnel barrier layer 215. In the absence of an externalmagnetic field, the free layer 210 has its magnetization oriented in thedirection shown by arrow 212, that is, generally perpendicular to themagnetization direction of the pinned layer 220 shown by arrow 222 (tailof an arrow pointing into the plane of the paper). A first lead 260 anda second lead 265 formed in contact with first electrode 204 and secondelectrode 202, respectively, provide electrical connections for the flowof sensing current I_(S) from a current source 270 to the MTJ sensor200. Because the sensing current is perpendicular to the plane of thesensor layers, the MTJ sensor 200 is known as acurrent-perpendicular-to-plane (CPP) sensor. A signal detector 280,typically including a recording channel such as a partial-responsemaximum-likelihood (PRML) channel, connected to the first and secondleads 260 and 265 senses the change in resistance due to magnetizationchanges induced in the free layer 210 by the external magnetic field.

Two types of current-perpendicular-to-plane (CPP) sensors have beenextensively explored for magnetic recording at ultrahigh densities (≧20Gb/in²). One is a GMR spin valve sensor and the other is a MTJ sensor.Two challenging issues are encountered when the CPP sensor is used forever increasing magnetic recording densities. First, the GMR coefficientmay not be high enough to ensure adequate signal amplitude as the sensorwidth is decreased and second, magnetic stabilization of the sense layercan be difficult due to the use of insulating layers to avoid currentshorting around the active region of the sensor. A dual CPP sensor canbe used to provide increased magnetoresistive response to a signal fielddue to the additive response of the two sensors. IBM's U.S. Pat. No.5,287,238 granted to Baumgart et al. discloses a dual CIP SV sensor.However, sensor stability still remains a major concern.

There is a continuing need to increase the GMR coefficient and reducethe thickness of GMR sensors while improving sensor stability. Anincrease in the GMR coefficient and reduced sensor geometry equates tohigher bit density (bits/square inch of the rotating magnetic disk) readby the read head.

SUMMARY OF THE INVENTION

It is an object of the present invention to disclose a dualcurrent-perpendicular-to-plane (CPP) spin valve (SV) sensor withimproved sensor layer stabilization.

It is another object of the present invention to disclose a dual CPP SVsensor having a longitudinal bias stack between a first SV stack and asecond SV stack to provide improved stabilization of the sense (free)layers of the first and second SV stacks.

It is a further object of the present invention to disclose a dual CPPSV sensor having a longitudinal bias stack comprising a first decouplinglayer, a first ferromagnetic (FM1) layer, an antiferromagnetic (AFM)layer, a second ferromagnetic (FM2) layer and a second decoupling layerdisposed between the sense layers of first and second SV stacks.

It is yet another object of the present invention to disclose a dual CPPSV sensor having a longitudinal bias stack disposed between first andsecond SV stacks to provide three flux closures for improved sensorstability. A first flux closure provides stability of the first SVstack, a second flux closure provides stability of the second SV stack,and a third flux closure provides cancellation of demagnetizing fieldsfrom first and second antiparallel (AP)-pinned layers of the dual SVsensor.

In accordance with the principles of the present invention, there isdisclosed a preferred embodiment of the present invention wherein a dualCPP SV sensor comprises a first SV stack, a second SV stack and alongitudinal bias stack disposed between first and second sense layersof the dual SV sensor. The first SV stack comprises a firstantiferromagnetic (AFM1) layer, a first AP-pinned layer, a firstconductive spacer layer and a first sense layer. The second SV stackcomprises a second antiferromagnetic (AFM2) layer, a second AP-pinnedlayer, a second conductive spacer layer and a second sense layer. Thelongitudinal bias stack comprises a third antiferromagnetic (AFM3) layersandwiched between a first ferromagnetic (FM1) layer and a secondferromagnetic (FM2) layer, and first and second decoupling layers inlaminar contact with the FM1 and FM2 layers, respectively.

The AFM1 and AFM2 layers are set by annealing the SV sensor at elevatedtemperature (about 280° C.) in a large magnetic field (about 10,000 Oe)oriented in a transverse direction perpendicular to an air bearingsurface (ABS) to orient the magnetizations of the first and secondAP-pinned layers. The AFM3 layer, formed of antiferromagnetic materialhaving a lower blocking temperature (temperature at which the pinningfield reaches zero Oe) than AFM1 and AFM2, is set by the annealing butis reset by a second annealing step at a lower temperature (about 240°C.) in a much smaller magnetic field (about 200 Oe) oriented in alongitudinal direction parallel to the ABS to reorient themagnetizations of the FM1 and FM2 layers from the transverse to thelongitudinal direction without reorienting magnetizations of the firstand second AP-pinned layers. After the two annealing steps, themagnetizations of the first and second AP-pinned layers are orientedperpendicular to the ABS with net magnetic moments canceling each other,and the magnetizations of the FM1 and FM2 layers are oriented in thelongitudinal direction. The magnetization of the FM1 layer forms a fluxclosure with the magnetization of the first sense layer and themagnetization of the FM2 layer forms a flux closure with themagnetization of the second sense layer. The first and second senselayers can be stabilized through magnetostatic interactions induced fromthe first and second flux closures, respectively.

The above as well as additional objects, features, and advantages of thepresent invention will become apparent in the following detaileddescription.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and advantages of the presentinvention, as well as the preferred mode of use, reference should bemade to the following detailed description read in conjunction with theaccompanying drawings. In the following drawings, like referencenumerals designate like or similar parts throughout the drawings.

FIG. 1 is an air bearing surface view, not to scale, of a prior art SVsensor;

FIG. 2 is an air bearing surface view, not to scale, of a prior artmagnetic tunnel junction sensor;

FIG. 3 is a simplified diagram of a magnetic recording disk drive systemusing the dual CPP SV sensor of the present invention;

FIG. 4 is a vertical cross-section view, not to scale, of a “piggyback”read/write head;

FIG. 5 is a vertical cross-section view, not to scale, of a “merged”read/write head;

FIG. 6 is an air bearing surface view, not to scale, of a preferredembodiment of a dual CPP SV sensor according to the present invention;

FIG. 7 is an air bearing surface view, not to scale, of anotherembodiment of a dual CPP SV sensor according to the present invention;and

FIG. 8 is an air bearing surface view, not to scale, of an embodiment ofa hybrid SV/MTJ sensor according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The following description is the best embodiment presently contemplatedfor carrying out the present invention. This description is made for thepurpose of illustrating the general principles of the present inventionand is not meant to limit the inventive concepts claimed herein.

Referring now to FIG. 3, there is shown a disk drive 300 embodying thepresent invention. As shown in FIG. 3, at least one rotatable magneticdisk 312 is supported on a spindle 314 and rotated by a disk drive motor318. The magnetic recording media on each disk is in the form of anannular pattern of concentric data tracks (not shown) on the disk 312.

At least one slider 313 is positioned on the disk 312, each slider 313supporting one or more magnetic read/write heads 321 where the head 321incorporates the dual SV sensor of the present invention. As the disksrotate, the slider 313 is moved radially in and out over the disksurface 322 so that the heads 321 may access different portions of thedisk where desired data are recorded. Each slider 313 is attached to anactuator arm 319 by means of a suspension 315. The suspension 315provides a slight spring force which biases the slider 313 against thedisk surface 322. Each actuator arm 319 is attached to an actuator 327.The actuator as shown in FIG. 3 may be a voice coil motor (VCM). The VCMcomprises a coil movable within a fixed magnetic field, the directionand speed of the coil movements being controlled by the motor currentsignals supplied by a controller 329.

During operation of the disk storage system, the rotation of the disk312 generates an air bearing between the slider 313 (the surface of theslider 313 which includes the head 321 and faces the surface of the disk312 is referred to as an air bearing surface (ABS)) and the disk surface322 which exerts an upward force or lift on the slider. The air bearingthus counterbalances the slight spring force of the suspension 315 andsupports the slider 313 off and slightly above the disk surface by asmall, substantially constant spacing during normal operation.

The various components of the disk storage system are controlled inoperation by control signals generated by the control unit 329, such asaccess control signals and internal clock signals. Typically, thecontrol unit 329 comprises logic control circuits, storage chips and amicroprocessor. The control unit 329 generates control signals tocontrol various system operations such as drive motor control signals online 323 and head position and seek control signals on line 328. Thecontrol signals on line 328 provide the desired current profiles tooptimally move and position the slider 313 to the desired data track onthe disk 312. Read and write signals are communicated to and from theread/write heads 321 by means of the recording channel 325. Recordingchannel 325 may be a partial response maximum likelihood (PMRL) channelor a peak detect channel. The design and implementation of both channelsare well known in the art and to persons skilled in the art. In thepreferred embodiment, the recording channel 325 is a PMRL channel.

The above description of a typical magnetic disk storage system, and theaccompanying illustration of FIG. 3 are for representation purposesonly. It should be apparent that disk storage systems may contain alarge number of disks and actuator arms, and each actuator arm maysupport a number of sliders.

FIG. 4 is a side cross-sectional elevation view of a “piggyback”read/write head 400, which includes a write head portion 402 and a readhead portion 404, the read head portion employing a dual SV sensor 406according to the present invention. The SV sensor 406 is sandwichedbetween ferromagnetic first and second shield layers 412 and 414 at theABS 440. A nonmagnetic insulating layer 409 is sandwiched between thefirst and second shield layers 412 and 414 in the region behind thesensor extending away from the ABS to prevent shorting between theshield layers. In response to external magnetic fields, the resistanceof the SV sensor 406 changes. A sense current I_(S) conducted throughthe sensor causes these resistance changes to be manifested as voltagechanges. These voltage changes are then processed as readback signals bythe processing circuitry of the data recording channel 325 shown in FIG.3.

The write head portion 402 of the magnetic read/write head 400 includesa coil layer 416 sandwiched between first and second insulating layers418 and 420. A third insulating layer 422 maybe employed for planarizingthe head to eliminate ripples in the second insulating layer 420 causedby the coil layer 416. The first, second and third insulating layers arereferred to in the art as an insulation stack. The coil layer 416 andthe first, second and third insulating layers 418, 420 and 422 aresandwiched between first and second pole piece layers 424 and 426. Thefirst and second pole piece layers 426 are magnetically coupled at aback gap 428 and have first and second pole tips 430 and 432 which areseparated by a write gap layer 434 at the ABS 440. An insulating layer436 is located between the second shield layer 414 and the first polepiece layer 424. Since the second shield layer 414 and the first polepiece layer 424 are separate layers, this read/write head is known as a“piggyback” read/write head.

FIG. 5 is the same as FIG. 4 except the second shield layer 414 and thefirst pole piece layer 424 are a common layer. This type of read/writehead is known as a “merged” head 500. The insulation layer 436 of thepiggyback head in FIG. 4 is omitted in the merged head 500 of FIG. 5.

FIRST EXAMPLE

FIG. 6 shows an air bearing surface (ABS) view, not to scale, of a dualCPP spin valve (SV) sensor 600 according to a preferred embodiment ofthe present invention. The SV sensor 600 comprises end regions 604 and606 separated from each other by a central region 602. The seed layer614 is a layer deposited to modify the crystallographic texture or grainsize of the subsequent layers, and may not be needed depending on thesubsequent layer. A first SV stack 608 deposited over the seed layer 614comprises a first antiferromagnetic (AFM1) layer 616, a first AP-pinnedlayer 617, an conductive first spacer layer 624 and a first sense layer625. The first AP-pinned layer 617 is formed of two ferromagnetic layers618 and 622 separated by an antiparallel coupling (APC) layer 620. TheAPC layer is formed of a nonmagnetic material, preferably ruthenium(Ru), that allows the two ferromagnetic layers 618 and 622 to bestrongly antiparallel-coupled together. The AFM1 layer 616 has athickness at which the desired exchange properties are achieved,typically 100–300 Å.

A longitudinal bias stack 610 sequentially deposited over the first SVstack 608 comprises a first decoupling layer 629, a first ferromagnetic(FM1) layer 630, a third antiferromagnetic (AFM3) layer 632, a secondferromagnetic (FM2) layer 634 and a second decoupling layer 633. Asecond SV stack 612 deposited over the longitudinal bias stack 610comprises a second sense layer 639, a second conductive spacer layer640, a second AP-pinned layer 641 and a second antiferromagnetic (AFM2)layer 648. The second AP-pinned layer 641 is formed of two ferromagneticlayers 642 and 646 separated by an antiparallel coupling (APC) layer644. The APC layer is formed of a nonmagnetic material, preferablyruthenium (Ru), that allows the two ferromagnetic layers 642 and 646 tobe strongly anti-parallel coupled together. The AFM2 layer 648 has athickness at which the desired exchange properties are achieved,typically 100–300 Å. A cap layer 650, formed on the AFM2 layer 648,completes the central region 602 of the dual SV sensor 600.

The AFM1 layer 616 is exchange-coupled to the first AP-pinned layer 617to provide a pinning field to pin the magnetizations of the twoferromagnetic layers of the first AP-pinned layer perpendicular to theABS as indicated by an arrow tail 619 and an arrow head 623 pointinginto and out of the plane of the paper, respectively. The first senselayer 625 has a magnetization 627 that is free to rotate in the presenceof an external (signal) magnetic field. The magnetization 627 of thefirst sense layer 625 is preferably oriented parallel to the ABS in theabsence of an external magnetic field.

The AFM2 layer 648 is exchange coupled to the second AP-pinned layer 641to provide a pinning magnetic field to pin the magnetizations of the twoferromagnetic layers of the second AP-pinned layer perpendicular to theABS as indicated by an arrow head 643 and an arrow tail 645 pointing outof and into the plane of the paper, respectively. The second sense layer639 has a magnetization 637 that is free to rotate in the presence of anexternal (signal) magnetic field. The magnetization 637 of the secondsense layer 639 is preferably oriented parallel to the ABS in theabsence of an external magnetic field.

The AFM3 layer 632 is exchange coupled to the FM1 layer 630 and the FM2layer 634 to provide pinning fields to pin the magnetizations 631 and635, respectively, parallel to the plane of the ABS. The magnetizations631 and 635 provide longitudinal bias fields which form flux closureswith the first and second sense layers 625 and 639, respectively, tostabilize the first and second sense layers 625 and 639.

First and second shield layers 652 and 654 adjacent to the seed layer614 and the cap layer 650, respectively, provide electrical connectionsfor the flow of a sensing current I_(S) from a current source 660 to theSV sensor 600. A signal detector 670 which is electrically connected tothe first and second shield layers 652 and 654 senses the change inresistance due to changes induced in the sense layers 625 and 639 by theexternal magnetic field (e.g., field generated by a data bit stored on adisk). The external field acts to rotate the magnetizations of the senselayers 625 and 639 relative to the magnetizations of the pinned layers622 and 642 which are preferably pinned perpendicular to the ABS. Thesignal detector 670 preferably comprises a partial response maximumlikelihood (PRML) recording channel for processing the signal detectedby SV sensor 600. Alternatively, a peak detect channel or a maximumlikelihood channel (e.g., 1,7 ML) may be used. The design andimplementation of the aforementioned channels are known to those skilledin the art. The signal detector 670 also includes other supportingcircuitries such as a preamplifier (electrically placed between thesensor and the channel) for conditioning the sensed resistance changesas is known to those skilled in the art.

The SV sensor 600 is fabricated in an integrated ion beam/DC magnetronsputtering system to sequentially deposit the multilayer structure shownin FIG. 6. The sputter deposition process is carried out in the presenceof a longitudinal magnetic field of about 40 Oe. The first shield layer652 formed of Ni—Fe having a thickness of 10000 Å is deposited on asubstrate 601. The seed layer 614 is a bilayer with a first sublayer oftantalum (Ta) having a thickness of 30 Å and a second sublayer of Ni—Fehaving a thickness of 10 Å deposited on the first shield layer 652. Thefirst SV stack 608 is formed on the seed layer by sequentiallydepositing the AFM1 layer 616 of Pt—Mn having a thickness of about 160Å, the ferromagnetic layer 618 of Co—Fe having a thickness of about 12Å, the APC layer 620 of ruthenium (Ru) having a thickness of about 8 Å,the ferromagnetic layer 622 of Co—Fe having a thickness of about 18 Å,the conductive first spacer layer 624 of Cu—O having a thickness ofabout 22 Å, and the first sense layer 625 of Co—Fe having a thickness ofabout 18 Å. The first spacer layer 624 is formed by depositing a copper(Cu) film with DC-magnetron sputtering from a pure Cu target in amixture of argon and oxygen gases of 2.985 and 0.015 mTorr,respectively, and then exposing to a mixture of argon and oxygen gasesof 2.94 and 0.06 mTorr, respectively, for 4 minutes. This optimum insitu oxidation is incorporated into this Cu—O formation process forreducing ferromagnetic coupling between the sense and pinned layers.

The longitudinal bias stack 610 is formed on the first SV stack 608 bysequentially depositing the first decoupling layer 629 comprising afirst sublayer 626 of Cu—O having a thickness of about 10 Å and a secondsublayer 628 of ruthenium (Ru) having a thickness of about 20 Å, the FM1layer 630 of Co—Fe having a thickness of about 24 Å, the AFM3 layer 632of Ir—Mn having a thickness of about 60 Å, the FM2 layer 634 of Co—Fehaving a thickness of about 24 Å, and the second decoupling layer 633comprising a first sublayer 636 of ruthenium (Ru) having a thickness ofabout 20 Å and a second sublayer 638 of Cu—O having a thickness of about10 Å. The Cu—O sublayers 626 and 638 are formed by depositing a copper(Cu) film with DC-magnetron sputtering from a pure Cu target in amixture of argon and oxygen gases of 2.985 and 0.015 mTorr,respectively, and then exposing to a mixture of argon and oxygen gasesof 2.94 and 0.06 mTorr, respectively, for 4 minutes. The Cu—O filmsfacilitate the sense layers to exhibit good soft magnetic properties.

The second SV stack 612 is formed on the longitudinal bias stack 610 bysequentially depositing the second sense layer 639 of Co—Fe having athickness of about 18 Å, the conductive second spacer layer 640 of Cu—Ohaving a thickness of about 22 Å, the ferromagnetic layer 642 of Co—Fehaving a thickness of about 18 Å, the APC layer 644 of ruthenium (Ru)having a thickness of about 8 Å, the ferromagnetic layer 646 of Co—Fehaving a thickness of about 12 Å, and the AFM2 layer 648 of Pt—Mn havinga thickness of about 160 Å. The spacer layer 640 is formed by depositinga copper (Cu) film with DC-magnetron sputtering from a pure Cu target ina mixture of argon and oxygen gases of 2.985 and 0.015 mTorr,respectively, and then exposing to a mixture of argon and oxygen gasesof 2.94 and 0.06 mTorr, respectively, for 4 minutes. This optimum insitu oxidation is incorporated into this Cu—O formation process forreducing ferromagnetic coupling fields between the sense and pinnedlayers. The cap layer 650 is bilayer with a first sublayer of ruthenium(Ru) having a thickness of 40 Å and a second sublayer of tantalum (Ta)having a thickness of 30 Å formed over the AFM2 layer 648.

The second shield layer 654 formed of Ni—Fe having a thickness of 10000Å is deposited over the cap layer 650. An insulating layer 656 formed ofAl₂O₃ deposited between the first shield layer 652 and the second shieldlayer 654 provides electrical insulation between the shields/leads andprevents shunting of the sense current around the active region 602 ofthe dual SV sensor 600.

After the deposition of the central portion 602 is completed, the SVsensor is annealed for 2 hours at 280° C. in the presence of a magneticfield of about 10,000 Oe in a transverse direction perpendicular to theABS and is then cooled while still in the magnetic field to set theexchange coupling of the AFM1 and AFM2 layers 616 and 648 with theAP-pinned layers 617 and 641, respectively, so that the magnetizationsin the two AP-pinned layers are perpendicular to the ABS with netmagnetic moments canceling each other. This results in cancellation ofthe demagnetization fields between the the AP-pinned layers 617 and 641.

After the first anneal, a second anneal is carried out for 2 hours at240° C. in the presence of a magnetic field of 200 Oe in a longitudinaldirection parallel to the ABS. Because the blocking temperature of thePt—Mn antiferromagnetic material (>360° C.) of the AFM1 and AFM2 layersis higher than 240° C., the magnetizations of the first and secondAP-pinned layers 617 and 641 are not rotated while the magnetizations631 and 635 in the longitudinal bias stack are oriented in thelongitudinal direction due to the lower (less than 240° C.) blockingtemperature of the Ir—Mn antiferromagnetic material of the AFM3 layer.After the second anneal, the magnetization 631 of the FM1 layer 630forms a flux closure with the magnetization 627 of the first sense layer625 providing stability for the first sense layer 625. Similarly, themagnetization 635 of the FM2 layer 634 forms a flux closure with themagnetization 637 of the second sense layer 639 providing stability ofthe second sense layer 639.

The Cu—O/Ru and Ru/Cu—O films are used as first and second decouplinglayers 629 and 633. Either one of the Cu—O or Ru films is not used aloneas a decoupling layer since strong exchange coupling occurs acrosseither film and full decoupling can only be attained when the filmthickness is far greater than 30 Å. In order to attain strongmagnetostatic interactions from the flux closures, the decoupling layerthickness is preferred to be as small as possible, but not to be toosmall to induce the exchange coupling. The Cu—O film of the decouplinglayers is adjacent to the Co—Fe sense layers to promote good softmagnetic properties. The Ru film of the decoupling layers is also usedas a seed layer for the Co—Fe/Ir—Mn/Co—Fe longitudinal bias layers topromote high unidirectional anisotropy fields (H_(UA)).

In this preferred embodiment, the Co—Fe/Ir—Mn/Co—Fe film stack is usedfor antiferromagnetic stabilization of the dual SV sensors.Alternatively, a Ni—Fe(10 Å)/Co—Pt(40 Å)/Ni—Fe(10Å) film stack can beused to replace the Co—Fe/Ir—Mn/Co—Fe film stack for hard magneticstabilization. The Ni—Fe film is adjacent to the Co—Pt film in order toreduce stray fields from the Co—Pt film and improve its squareness. Inthis alternate embodiment, the second anneal used to longitudinallyorient the magnetizations of the Co—Fe/Ir—Mn/Co—Fe stack is eliminated,but magnetic setting of the Ni—Fe/Co—Pt/Ni—Fe stack in a field of 3 kOemust be conducted at room temperature after the head fabricationprocess.

SECOND EXAMPLE

FIG. 7 shows an air bearing surface (ABS) view, not to scale, of a CPPdual spin valve (SV) sensor 700 according to another embodiment of thepresent invention. The dual SV sensor 700 is the same as the dual SVsensor 600 shown in FIG. 6 except that in order to achieve a read gapthickness of 50 nm the AFM1 and AFM2 layers 616 and 648 have beeneliminated and the AFM3 layer 632 of the longitudinal bias stack 610 hasbeen replaced by an AFM3 layer 716 of Pt—Mn having a thickness of 160 Å.The dual SV sensor 700 comprises a first SV stack 708, a second SV stack712 and a longitudinal bias stack 710 disposed between the first andsecond SV stacks 708 and 712. In this embodiment the first SV stack 708is the same as SV stack 608 without the AFM1 layer 616 and the second SVstack 712 is the same as SV stack 612 without the AFM2 layer 648. Thelongitudinal bias stack 710 is the same as bias stack 610 with the AFM3layer of Ir—Mn replaced with an AFM3 layer 716 of Pt—Mn having athickness of 160 Å.

The SV sensor 700 is fabricated in an integrated ion beam/DC magnetronsputtering system to sequentially deposit the multilayer structure shownin FIG. 7. The deposition process is the same as the process used tofabricate the SV sensor 600.

After the deposition of the central portion 602 is completed, the SVsensor 700 is annealed for 2 hours at 280° C. in the presence of amagnetic field of 200 Oe in a longitudinal direction parallel to theABS. The magnetic field is higher than the uniaxial anisotropy fieldH_(K) (≦20 Oe) of the as-deposited Co—Fe/Pt—Mn/Co—Fe films so thatstrong exchange coupling in the Co—Fe/Pt—Mn/Co—Fe films can be developedin the longitudinal direction parallel to the ABS during annealing. Themagnetic field is less than the spin flop field H_(SF) (≧1 kOe) of thefirst and second AP-pinned layers 617 and 641 so that strongantiparallel coupling across the Ru APC layers in the first and secondAP-pinned layers 617 and 641 is not interrupted during annealing.

Although the Pt—Mn AFM layers are not used in the first and second SVstacks 708 and 712 to produce H_(UA) for transverse pinning, thetransverse pinning can still be attained due to a strong spin-flop field(H_(SP)) induced from antiparallel coupling across the Ru APC layers.The transverse pinning can be further reinforced if the Co—Fe filmsadjacent to the Ru APC layers have a high intrinsic uniaxial anisotropyfield (H_(K)) and a high positive saturation magnetostriction (λ_(S)).The high λ_(S) is needed to stress-induce a high extrinsic uniaxialanisotropy field (H_(K)′), determined from H_(K)′=3(λ_(S)/M_(S))σ aftersensor lapping. The Co₉₀—Fe₁₀ (in atomic %) commonly used for theferromagnetic layers of the AP-pinned layers 617 and 641 has an H_(K) of16 Oe. When the Fe content is increased to 20 at. %, H_(K) becomes 30 Oeand the λ_(S) increases to 35.1×10⁻⁶ (corresponding to 142 Oe). Hence,in this alternative embodiment, a Co—Fe film with an Fe content of 20at. % or higher (up to 50 at. %) is preferably used for theferromagnetic layers of the AP-pinned layers.

Although the total uniaxial anisotropy field H_(K)+H_(K)′ (172.5 Oe) isnot as high as H_(UA) (600 Oe) and H_(SP) (900 Oe), it has two majorunique features, leading it to play an important role in providingtransverse pinning. First, H_(K)+H_(K)′ is determined only from theCo—Fe film itself, while H_(UA) and H_(SP) are determined not only fromthe Co—Fe film, but also from its adjacent Ru and Pt—Mn films. As aresult, the temperature dependence of H_(K)+H_(K)′ is determined by theCurie temperature of the Co—Fe film (˜700° C.), while the temperaturedependence of H_(UA) is determined by the blocking temperature of theexchange-coupled Pt—Mn/Co—Fe films (˜360° C.), and the temperaturedependence of H_(SP) is determined by the critical temperature of theantiparallel-coupled Co—Fe/Ru/Co—Fe films. Since the Curie temperatureis much higher than the blocking and critical temperatures, H_(K)+H_(K)′can remain nearly unchanged at elevated sensor operation temperatures(˜180° C.). Thus H_(K)+H_(K)′ may play a crucial role in improvingthermal stability. Second, H_(K)+H_(K)′ substantially reduces edgecurling effects of magnetizations of the ferromagnetic films of theAP-pinned layers. The reduction in the edge curling effects results inmore uniform magnetization along the sensor height, therefore providingbetter flux closure to cancel magnetization more efficiently. Hence,even without the use of the Pt—Mn film for transverse pinning, thetransverse pinning field resulting from H_(SP), H_(K) and H_(K)′ shouldbe high enough for proper sensor operation.

THIRD EXAMPLE

FIG. 8 shows an air bearing surface (ABS) view, not to scale, of a CPPhybrid spin valve (SV)/magnetic tunnel junction (MTJ) sensor 800according to a another embodiment of the present invention. The hybridSV/MTJ sensor 800 is the same as the dual SV sensor 600 shown in FIG. 6except that one of the two SV stacks 608 and 612 is replaced with amagnetic tunnel junction (MTJ) stack. In the embodiment shown in FIG. 8,the second SV stack 612 has been replaced with an MTJ stack 812.However, alternatively, the first SV stack 608 may be replaced with anMTJ stack to form an alternative hybrid MTJ/SV sensor.

The SV/MTJ sensor 800 comprises an SV stack 608, an MTJ stack 812 and alongitudinal bias stack 610 disposed between the SV stack 608 and andthe MTJ stack 812. In this embodiment the SV stack 608 and thelongitudinal bias stack 610 are identical to the first SV andlongitudinal bias stacks of the preferred embodiment shown in FIG. 6.The MTJ stack 812 deposited over the longitudinal bias stack 610comprises a second sense layer 639, a nonconductive tunnel barrier layer840, a second AP-pinned layer 641 and a second antiferromagnetic (AFM2)layer 648. Only the tunnel barrier layer 840 which replaces theconductive second spacer layer 640 of the SV sensor 600 is differentfrom the layers forming the SV sensor 640. The tunnel barrier layer 840of Al—O having a thickness of about 6 Å is formed on the second senselayer 639 by depositing an aluminum (Al) film with DC-magnetronsputtering from a pure Al target in an argon gas of 3 mTorr, and thenexposing to an oxygen gas of 2 Torr for 4 minutes. This optimal in situoxidation is incorporated into this Al—O formation process for attaininga high tunneling magnetoresistance and a low junction resistance. Thesecond AP-pinned layer 641 and the AFM2 layer 648 are sequentiallydeposited on the tunnel junction layer 840 to complete the fabricationof the MTJ stack 612. All other processing steps are identical to thosedescribed above with respect to fabrication of the SV sensor 600. Theresponse of the hybrid dual SV/MTJ sensor 800 to an external magneticsignal is the sum of the response of the SV stack 608 and the responseof the MTJ stack 812.

Alternatively, for the hybrid MTJ sensor 800, the AFM1 and AFM2 layersformed of Pt—Mn used in the first and second stacks can be eliminated,and the Ir—Mn film used for AFM3 in the longitudinal bias stack may alsobe replaced with a Pt—Mn film as described in the second example.

While the present invention has been particularly shown and describedwith reference to the preferred embodiments, it will be understood bythose skilled in the art that various changes in form and detail may bemade without departing from the spirit, scope and teaching of theinvention. Accordingly, the disclosed invention is to be consideredmerely as illustrative and limited only as specified in the appendedclaims.

1. A dual spin valve (SV) sensor having an air bearing surface (ABS),comprising: a first spin valve (SV) stack having a free layermagnetization that is biased in a direction that is substantiallyparallel to the ABS; a second spin valve (SV) stack; and a longitudinalbias stack disposed between said first and second SV stacks, saidlongitudinal bias stack further comprising: a first ferromagnetic (FM1)layer having a magnetization that is pinned in a direction substantiallyparallel with the ABS; a second ferromagnetic (FM2) layer having amagnetization that is pinned in a direction substantially parallel withthe ABS; a layer of antiferromagnetic material disposed between saidFM1and FM2 layers; a first decoupling layer disposed between said FM1layer and said first spin valve stack; and a second decoupling layerdisposed between said FM2 layer and said second spin valve stack.
 2. Adual spin valve (SV) sensor, comprising: a first spin valve (SV) meansfor providing a first readback signal in response to a magnetic signalfield, said first SV means including a first sense layer means, thefirst sense layer means having a magnetization that is biased in a firstdirection, but that is free to rotate in response to said magneticsignal field; a second spin valve (SV) means for providing a secondreadback signal in response to said magnetic signal field, said secondSV means including a second sense layer means, the second sense layermeans having a magnetization that is biased in the first direction, butthat is free to rotate in response to said magnetic signal field; and abias means for providing longitudinal bias fields at said first andsecond sense layer means to stabilize said first and second SV means,said bias means disposed between said first and second sense layermeans; said bias means further comprising: a first ferromagnetic (FM1)layer, the FM1 layer being magnetostatically coupled with the firstsense layer means and having a magnetization that is pinned in adirection opposite to the magnetization of the first sense layer means;a second ferromagnetic (FM2) layer, the FM2 layer beingmagnetostatically coupled with the second sense layer means and having amagnetization that is pinned in a direction opposite to themagnetization of the second sense layer means; a layer ofantiferromagnetic material disposed between said FM1 and FM2 layers; afirst decoupling layer disposed between said FM1 layer and said firstspin valve means; and a second decoupling layer disposed between saidFM2 layer and said second spin valve means.
 3. A magnetic read/writehead, comprising: a write head including: at least one coil layer and aninsulation stack, the coil layer being embedded in the insulation stack;first and second pole piece layers connected at a back gap and havingpole tips with edges forming a portion of an air bearing surface (ABS);the insulation stack being sandwiched between the first and second polepiece layers; and a write gap layer sandwiched between the pole tips ofthe first and second pole piece layers and forming a portion of the ABS;a read head including: a dual spin valve (SV) sensor, the dual SV sensorbeing sandwiched between first and second shield layers, the dual SVsensor comprising: a first spin valve (SV) stack having a free layermagnetization that is biased in a direction that is substantiallyparallel to the ABS; a second spin valve (SV) stack; and a longitudinalbias stack disposed between said first and second SV stacks; and aninsulation layer disposed between the second shield layer of the readhead and the first pole piece layer of the write head, said longitudinalbias stack further comprising: a first ferromagnetic (FM1) layer; asecond ferromagnetic (FM2) layer; a layer of antiferromagnetic materialdisposed between and exchange coupled with said FM1 and FM2 layers; afirst decoupling layer disposed between said FM1 layer and said firstspin valve stack; and a second decoupling layer disposed between saidFM2 layer and said second spin valve stack; and wherein the FM1 and FM2layers each have a magnetization that is pinned in a direction that isparallel with the ABS.
 4. A magnetic read/write head, comprising: awrite head including: at least one coil layer and an insulation stack,the coil layer being embedded in the insulation stack; first and secondpole piece layers connected at a back gap and having pole tips withedges forming a portion of an air bearing surface (ABS); the insulationstack being sandwiched between the first and second pole piece layers;and a write gap layer sandwiched between the pole piece layers andforming a portion of the ABS; a read head including: a dual spin valve(SV) sensor, the SV sensor being sandwiched between first and secondshield layers, the SV sensor comprising: a first spin valve (SV) meansfor providing a first read back signal in response to a magnetic signalfield, said first SV means including a first sense layer meansresponsive to said magnetic signal field and having a magnetization thatis biased in a direction that is parallel with the ABS; a second spinvalve (SV) means for providing a second readback signal in response tosaid magnetic signal field, said second SV means including a secondsense layer means responsive to said magnetic signal field having amagnetization that is biased in a direction that is parallel to the ABS;and a bias means for providing longitudinal bias fields at said firstand second sense layer means to stabilize said first and second SVmeans, said bias means disposed between said first and second senselayer means; said bias means comprising: a first ferromagnetic (FM1)layer having a magnetization that is pinned in a direction that isparallel with the ABS; a second ferromagnetic (FM2) layer having amagnetization that is pinned in a direction that is parallel with theABS; a layer of antiferromagnetic material disposed between and exchangecoupled with said FM1 and FM2 layers; a first decoupling layer disposedbetween said FM1 layer and said first sense layer means; and a seconddecoupling layer disposed between said FM2 layer and said second senselayer means; and an insulation layer disposed between the second shieldlayer of the read head and the first pole piece layer of the write head.5. A disk drive system comprising: a magnetic recording disk; a magneticread/write head for magnetically recording data on the magneticrecording disk and for sensing magnetically recorded data on themagnetic recording disk, said magnetic read/write head comprising: awrite head including at least one coil layer and an insulation stack,the coil layer being embedded in the insulation stack; first and secondpole piece layers connected at a back gap and having pole tips withedges forming a portion of an air bearing surface (ABS); the insulationstack being sandwiched between the first and second pole piece layers;and a write gap layer sandwiched between the pole tips of the first andsecond pole piece layers and forming a portion of the ABS; a read headincluding: a dual spin valve (SV) sensor, the SV sensor being sandwichedbetween first and second shield layers, the SV sensor comprising: afirst spin valve (SV) stack having a free layer magnetization that isbiased in a direction that is substantially parallel to the ABS; asecond spin valve (SV) stack; and a longitudinal bias stack disposedbetween said first and second SV stacks, the longitudinal bias stackfurther comprising: a first ferromagnetic (FM1) layer having amagnetization that is pinned in a direction that is parallel with theABS; a second ferromagnetic (FM2) layer having a magnetization that ispinned in a direction that is parallel with the ABS; a layer ofantiferromagnetic material disposed between and exchange coupled withsaid FM1 and FM2 layers; a first decoupling layer disposed between saidFM1 layer and said first spin valve stack; and a second decoupling layerdisposed between said FM2 layer and said second spin valve stack; and aninsulation layer disposed between the second shield layer of the readhead and the first pole piece layer of the write head; an actuator formoving said magnetic read/write head across the magnetic disk so thatthe read/write head may access different regions of the magneticrecording disk; and a recording channel coupled electrically to thewrite head for magnetically recording data on the magnetic recordingdisk and to the SV sensor of the read head for detecting changes inresistance of the SV sensor in response to magnetic fields from themagnetically recorded data.
 6. A disk drive system comprising: amagnetic recording disk; a magnetic read/write head for magneticallyrecording data on the magnetic recording disk and for sensingmagnetically recorded data on the magnetic recording disk, said magneticread/write head comprising: a write head including: at least one coillayer and an insulation stack, the coil layer being embedded in theinsulation stack; first and second pole piece layers connected at a backgap and having pole tips with edges forming a portion of an air beatingsurface (ABS); the insulation stack being sandwiched between the firstand second pole piece layers; and a write gap layer sandwiched betweenthe pole tips of the first and second pole piece layers and forming aportion of the ABS; a read head including: a dual spin valve (SV)sensor, the SV sensor being sandwiched between first and second shieldlayers, the SV sensor comprising: a first spin valve (SV) means forproviding a first readback signal in response to a magnetic signalfield, said first SV means including a first sense layer meansresponsive to said magnetic signal field and having a magnetization thatis biased in a direction that is parallel with the ABS; a second spinvalve (SV) means for providing a second readback signal in response tosaid a magnetic signal field, said second SV means including a secondsense layer means responsive to said magnetic signal field and having amagnetization that is biased in a direction parallel with the ABS; and abias means for providing longitudinal bias fields at said first andsecond sense layer means to stabilize said first and second SV means,said bias means disposed between said first and second sense layermeans, said bias means further comprising: a first ferromagnetic (FM1)layer having a magnetization that is pinned in a direction that isparallel with the ABS; a second ferromagnetic (FM2) layer having amagnetization that is pinned in a direction that is parallel with theAB$; a layer of antiferromagnetic material disposed between said FM1 andFM2 layers; a first decoupling layer disposed between said FM1 layer andsaid first spin valve means; and a second decoupling layer disposedbetween said FM2 layer and said second spin valve means; an insulationlayer disposed between the second shield layer of the read head and thefirst pole piece layer of the write head; and an actuator for movingsaid magnetic read/write head across the magnetic disk so that theread/write head may access different regions of the magnetic recordingdisk; and a recording channel coupled electrically to the write head formagnetically recording data on the magnetic recording disk and to the SVsensor of the read head for detecting changes in resistance of the SVsensor in response to magnetic fields from the magnetically recordeddata.